131 comptime chain composes

// Comptime calls COMPOSE. The fold pass consumes a chain of [comptime] heads
// to fixpoint — a bare-return impl evaluates (mul), a proc handler calls
// through the Stage A thunk table (bump), a subflow implementation walks
// (describe, producing via `-> expr` arm tails) — and each result splices
// into the next call's argument text. Only the runtime residue (the print)
// emits. mul(30,4)=120 -> bump=121 -> pick produces `big` -> describe=221.
~import std/io

~[comptime] tor mul { l: i64, r: i64 } -> i64
~mul -> l * r

~[comptime] tor bump { n: i64 } -> i64
~proc bump|zig {
    return n + 1;
}

~[comptime] tor pick { n: i64 }
| small i64
| big i64
~proc pick|zig {
    if (n < 100) return .{ .small = n };
    return .{ .big = n };
}

~[comptime] tor describe { n: i64 } -> i64
~describe = pick(n)
| small v -> v
| big v -> v + 100

~mul(l: 30, r: 4): m |> bump(n: m): b |> describe(n: b): d |> std/io:print.ln("{{ d:d }}")